MissCat, If you opt to respond back to him, reply "the cat is fine". Don't get chatty w/him. Keep your response short and sweet.
As for counseling, this is his counseling session to work on himself. He needs to figure himself out w/o you being a party to it right now. If he wants you to go, he'll ask you...but until then...allow him to do this on his own.
MLCers like to put out little notes to see just how vested we still are in them. It's also his way of finding out what you are doing and/or thinking because we tend to get our hopes up that by chatting w/them, they'll come to realize that they want back into the marriage. Most of the time, this is not the case. Don't take the bait.
He's purchasing things on the joint credit card. You are aware that if he doesn't come up w/the money to pay for those charges on the joint account that you will be responsible for them? As I may have advised earlier, you need to seriously think about separating the joint accounts before his spending gets out of hand and you are stuck w/the outstanding bills. You and only you can protect yourself financially. You can't rely on him doing the right thing. My advice, have your name removed from the joint accounts as quickly as you can. Please do not put this off because he can rack up the bills quite quickly and it appears that he has already started.
The ow doesn't care about you. All she cares about is having your h and his money. She knows that he's unhappy and she's going to be right there egging him on to do fun things and spending money on her. She doesn't care where the money comes. If it's not the ow we are thinking it is, it could very well be someone he's met. The ow is a needy individual and your h is looking to be the knight to save her.
The saying "Let go, let God" was posted on this forum by MGoBlue many, many years ago and it's still used today and it's used by others on other marriage forums as well.
Take each day as it comes and break it down into small parts so that you can handle things better. You are going to have good days and bad days. Allow the pain to wash over you and release it. If the your anger comes out to play, put it to good use, i.e., such as cleaning, walking, any type of physical exercise, but don't call him up and ream him another one. That will then be an excuse to help him justify why he left.
So, for now, keep the focus on you, your work, kitty and your finances.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.